Electronic motorized zone valve

ABSTRACT

An valve actuator in a hydronic heating and cooling system includes a motor for changing the position of a valve, a switch for switching power to the motor, and a sensor for detecting the arrival of the valve at a desired position and for stopping the motor without using a mechanical stop. The motor&#39;s power source includes a capacitive power source which can be used to drive the motor under low-power conditions. A worm gear is used in the drive train, and combined with a clutch assembly to permit the valve to be operated manually.

BACKGROUND OF THE INVENTION

The invention relates to actuators and zone valves for heating andcooling systems.

Zone valves are often utilized in hydronic heating and cooling systems.The zone valves isolate specific areas or “zones” of the system.Typically, each zone valve is controlled by a thermostat, which causesthe valve to open and close to achieve desired temperature changes.

Conventional zone valves are typically actuated by either a heat motoror an electric motor. In valves with a heat motor as the actuator, anelectrically heated element causes linear movement of an actuatingelement that, in turn, opens the valve. In valves with electric motors,the motor and associated gears move a valve member between closed andopen positions (e.g., a rubber plunger moved away from a seat or a ballelement moved through a 90 degree rotation).

Conventional motorized zone valve actuators employ a motor which isenergized in one direction by a source of power, held in somepredetermined position by a mechanical or electrical braking means, andthen returned to its original position by a spring.

Giordani, U.S. Pat. Nos. 5,131,623 and 5,540,414, describe zone valvesfor hydronic heating or cooling systems in which a motor-driven actuatorrotates a ball valve through about a 90° rotation, between closed andopened positions. The motor rotates the valve from its normal position,which may be either open or closed, to the opposite position, e.g., ifthe valve is normally closed, from the closed to the open position. Whenthe motor is de-energized, the valve is returned to its normal positionby a spring so configured that it provides sufficient restoring torqueto overcome the frictional torque of the ball valve.

Carson, U.S. Pat. No. 3,974,427, discloses a motor control apparatushaving an electric motor which is driven in one direction by analternating current power source and in the opposite direction by aspring. Holding or braking of the motor is accomplished by applying asource of direct current power to magnetize the motor and hold it in apredetermined position after the alternating current power source isremoved. This holding or braking action is removed by taking away thedirect current power source and momentarily applying an alternatingcurrent power source to the motor, thereby de-magnetizing or degaussingthe motor so that it is free to return to its initial condition underthe power of the spring.

Fukamachi, U.S. Pat. No. 4,621,789, discloses a valve mechanism in whichthe valve is prevented by a physical stopper from moving any furtherafter it has moved to an open or closed state.

Botting, et al, U.S. Pat. No. 5,085,401, discloses a valve actuator inwhich the motor makes an electrical contact after rotating apredetermined distance, causing deenergization of the motor.

Fukamachi, U.S. Pat. No. 4,754,949, discloses a valve actuator in whichthe rotation of the valve by a predetermined amount causes electricalcontacts to be turned off, stopping the rotation of the actuator motor.

Some motorized valve actuator systems employ a fail safe energy systemto provide power to the actuator motor in the event that the main powersource is lost. Strauss, U.S. Pat. No. 5,278,454, discloses anemergency, fail safe capacitive energy source and circuit which is usedto power an air damper actuator or a valve actuator. A sensor detectsloss of power to the valve actuator circuit or motor, activating aswitch which connects a bank of capacitors to the motor, with theappropriate polarity to drive the actuator back to its fail safeposition. No provision is made for interrupting the connection betweenthe capacitors and the motor when the fail safe position is reached, andthus the motor appears to work against a mechanical stop defining thefail safe position.

SUMMARY OF THE INVENTION

The invention features an actuator in which a sensor detects when thevalve has reached a desired position, and controls a switch that shutsoff the motor driving the valve. The invention makes it unnecessary torely on a mechanical stop or a return spring to put the valve in adesired position. For example, a valve can be moved from open to closedand from closed to open, without relying on a mechanical stop or returnspring. And switching a valve from normally-open to normally-closed canbe done simply by throwing a single switch.

In one aspect, the invention features an actuator for actuating a valvein a hydronic system, wherein the valve has a first position in whichfluid flow may occur along one path and a second position in which fluidflow is either blocked or may flow along another path. The actuatorincludes: a motor coupled to the valve, wherein rotation of the motorchanges the position of the valve from one of the first and secondpositions to the other of the positions; a switch controlling thedelivery of electrical power to the motor, the switch having a closedposition in which electrical power is delivered to the motor and an openposition in which power is not delivered; a sensor configured to detectthe arrival of the valve at the first and second positions; andcircuitry connected to the sensor and to the switch, the circuitry beingconfigured to respond to the detection by the sensor of the arrival ofthe valve at one of the first and second positions by opening the switchto stop delivery of power to the motor.

Preferred implementations of the invention may include one or more ofthe following features: The sensor may be configured so that the outputof the sensor changes state upon the arrival of the valve at a desiredposition. The sensor may have two states, and a change of state in itsoutput occurs at approximately the moment when the valve, having begunto move from one of the first and second positions, reaches the other ofthe positions. The motor may rotate the valve in a single direction. Anelectrical power storage element (e.g., a capacitor) can be included inthe actuator for providing power for driving the motor, sensor, andcircuitry (e.g., when power to the actuator is lost). The circuitry forcontrolling the actuator can be provided by an integrated circuit chip.The valve may be a ball valve. The sensor may be an optical sensor. Theactuator may have projections on a member that rotates with rotation ofthe valve and the projections may cause the sensor to become blocked andunblocked, and arrival of the valve at a position corresponds toblockage of the sensor by a projection either ceasing or beginning. Theactuator may include a clutch for manually rotating the valve, and theposition of the clutch may provide an indication of the angular positionof the valve. The actuator may include a worm gear drive between themotor and the valve. A default-position selection switch may be includedto enable the actuator and valve to be transformed from a normally-openvalve to a normally-closed valve by movement of an electrical switch.

In a second aspect, the invention feature a zone valve for use in ahydronic system, in which the valve includes a ball element; a valvecasing enclosing a ball element; a valve seat in contact with the ballelement and the valve casing, the valve seat having a notch to receivean O-ring; an O-ring installed in the notch; a metallic, springy washerpositioned in a compressed state within the valve casing in such aconfiguration as to provide an approximately constant force on the valveseat; and wherein the notch is shaped so that the axial force causes theO-ring installed in the notch to be compressed to improve a seal betweenthe valve seat and an internal bore of the valve casing.

In a third aspect, the invention features operating a hydronic valveactuator by, prior to initiating movement of the valve, determining thecharge on a capacitive power source and determining the energy requiredto complete the valve movement prescribed, and then deciding to initiatemovement only if the charge on the capacitive power source is sufficientto provide the energy required to complete the movement.

In a fourth aspect, the invention features a hydronic valve actuatorincluding a motor for driving the valve, wherein rotation of the motorchanges the position of the valve from one of the first and secondpositions to the other of the positions; a gear assembly coupling themotor to the valve, wherein the gear assembly includes a worm gear; anda knob shaped to be turned manually either by grasping or by use of atool; a clutch assembly connecting the knob to the valve stem and to thegear assembly, wherein the clutch assembly can be moved between engagedand disengaged modes, wherein in the engaged mode the gear assembly andworm gear are engaged with the valve stem so that the motor can turn thevalve, and in the disengaged mode the gear assembly and worm gear aredisengaged from the valve stem so that the valve can be turned using theknob.

Preferred implentations of this aspect of the invention may include oneor more of the following features: The clutch assembly may be disengagedby pushing the knob axially. The clutch assembly may include teeth ontwo rotating members that are separated by axial motion of the knob todisengage the clutch. The knob may have a marking indicating theposition of the valve.

Other features of the invention will be apparent from the followingdescription of preferred embodiments, including the drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a valve and actuator according tothe invention.

FIG. 2 is an isometric view of the interior of the actuator.

FIG. 3 is an isometric, exploded view of components of the clutchmechanism of the actuator.

FIGS. 4A-4D are diagrammatic views of the optical sensor and drivemember of the actuator in four different positions.

FIG. 5 is a schematic of the electronics of the actuator.

FIGS. 6-13 are flow charts of the processes followed by themicroprocessor in controlling the actuator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a preferred zone valve 10. Ball valve 12 is driven byactuator 14. The actuator is coupled to the valve body 26 (bronzeforging) by a rotate-to-lock fastening arrangement 23. Flat-sided stem16 extends from ball element 18 into a matching opening 19 in theactuator. The actuator is electrically operated, and has wires forcoupling it to conventional power and control circuitry.

Fluid flows through the ball valve in a conventional manner. When theball is in the open position, fluid flows through the ball element 18from port 37 a to port 37 b. The valve is bidirectional, and thus eitherof ports 37 a, 37 b can be an inlet or an outlet.

Ball element 18 (brass) seals against seats 20 a, 20 b (Teflon), whichare, in turn, sealed to the internal bore 25 of the valve forging byO-rings 22 a, 22 b, which sit in O-ring notches 21 a, 21 b. A wavywasher 30 (stainless steel) provides an axial force on the seats 20 a,20 b (the curvature of the washer is exaggerated in the drawing).Notches 21 a, 21 b are shaped so that the axial force compresses theO-rings, causing them to press outwardly against the bore of the valvecasing, to effect a seal between the valve seats and the bore. The wavywasher presses against backing ring 24 (stainless steel), which pressesagainst O-rings 22 a. By making the wavy washer out of a springymetallic material (e.g., stainless steel), it retains its resiliencyover time. As O-rings 22 a, 22 b compress over time, the wavy washerexpands while maintaining adequate axial force. Over the life of thevalve, the wavy washer will compensate for the tendency of the Teflonvalve seats to cold flow and/or wear; the washer will expand slightly,to maintain the seats in contact with the ball.

Referring to FIG. 2, a motor 40 turns a pinion 42, which in turn drivesa cluster gear 44, consisting of a large and small spur gear molded asone plastic part. Cluster gear 44 drives a second cluster gear 45,consisting of a small spur gear 47 and a worm gear 34 also molded as oneplastic part. The worm gear engages drive gear 31, which, in turn,rotates drive member 47, which, in turn, rotates valve stem 16. Theentire gear train (pinion gear 42 through drive gear 31) provides a960:1 increase in torque. The worm gear 34 and drive gear 31 provide an80:1 increase.

Referring to FIG. 3, the ball valve 12 may be manually opened and closedby depressing and turning a knob 70 (FIG. 3) exposed above the top cover(not shown) of the actuator. The knob is connected to stem 16 of theball valve via drive member 47, and can be manually disengaged fromdrive gear 31 using a clutch mechanism 38. Normally, valve clutch teeth48 on the drive member interlock with valve teeth 50 on the drive gear.A compression spring 32 (FIG. 1) wraps around shaft 49, and provides anupward force on drive member 47 to keep the teeth engaged. Manualmovement of the valve is not possible with the teeth engaged, as suchmovement would require that drive gear 31 turn worm gear 34 in reverse(the 80:1 torque ratio of the worm and drive gears prevents that fromhappening). To manually rotate the valve, the valve clutch teeth 48 aredisengaged from the valve teeth 50 by pressing downward on knob 70 (FIG.3) and rotating drive member 47. Because the drive member is directlyconnected to the valve stem 16, rotation of knob 70 results in rotationof the ball valve. Once the clutch is disengaged, the valve may berotated in either direction. After the valve has been manually rotatedto a desired position, pressure is removed from the knob, spring 32causes the clutch teeth to reengage. A valve position indicator 54 ismolded into knob 70, to provide a visual indication to the valveoperator of the current position of the valve. A notch 56 is provided inthe knob to permit a screwdriver, or other thin rigid object, to be usedto turn the valve.

The electronic circuitry controlling operation of the actuator dependson an optical sensor U2 (FIGS. 3 and 4A-4D) to determine the position ofthe valve. The sensor is positioned so its light path is alternatelyblocked and unblocked as drive member 47 is turned. Projections 72, 74extending from the drive member pass through the optical path of thesensor.

FIGS. 4A-4D illustrate operation of the sensor. Projections 72, 74 arepositioned on drive member 47 so that the sensor is blocked in twoquadrants of rotation of the drive member. Each of projections 72, 74blocks the optical sensor over 90° of travel, leaving 90° between themin which the sensor is not blocked. In operation, the circuitrycontrolling motor 40 will turn the motor on and keep it on until achange of state occurs at the optical sensor. E.g., if movement of thevalve were to begin with the drive member in the position shown in FIG.4A, in which the optical sensor is blocked by projection 72, movementwould continue for approximately 90 degrees of travel, until the drivemember rotated to the position shown in FIG. 4B, wherein projection 72has just moved out of the path of the optical sensor. (A natural lagbetween the moment that the sensor detects a change in state and actualcessation of movement assures that the actuator stops a small angulardisplacement beyond the position at which the optical sensor becameunblocked; this assures that vibration will not cause the sensor tobecome blocked again and restart.) This 90 degrees of movement wouldhave either opened or closed the ball valve. If further movement of theball valve were called for (e.g., if the valve were now open, and thecircuitry called for the actuator to close the valve), the motor wouldbe turned on and the valve would continue to rotate for approximatelyanother 90 degrees of travel to the position shown in FIG. 4C, at whichpoint the optical path is again blocked, this time by projection 74.

FIG. 5 is a schematic of the electronic circuitry of the actuator. Atthe heart of the circuitry is a microprocessor U1, which hasprogrammable pins GP0, GP1, GP2, GP3, GP4, and GP5, a power supply pinVdd, and a ground pin Vss. Power (24V AC) is supplied to the circuitrythrough two-pin connector CONN1. Typically, a 24V AC transformer isconnected to CONN1 through a thermostat. When the thermostat turns on,24V AC flows through CONN1 and into the power supply circuitry (diodeD1, resistors R1 and R2, and transistor Q1), which sets supply voltageVcc.

A capacitor C1 with a capacitance of 3.3 F is connected between Vcc andground. During normal operation, the capacitor C1 charges to 2.5V toprovide power to the motor 40, as described below. A switch SW1 is usedto configure the zone valve 10 to be either normally open or normallyclosed. The position of switch SW1 can be changed by an operator bymeans of a slide knob 58 accessible on the exterior of the actuatorassembly 14 (FIG. 2).

Power to optical sensor U2 is provided at pin GP0 of the microprocessorU1. When the light path to the optical sensor U2 is blocked, pin 4 ofthe sensor outputs a logical LO. When the light path is not blocked, pin4 outputs a logical HI.

A two-pin motor connector J1 provides power to motor 40. Supply voltageVcc is delivered at one pin. The other pin is connected to gatingtransistor Q2, which is in turn controlled by the microprocessor. Whenmicroprocessor pin GP4 is HI, transistor Q2 turns on, supplying power tothe motor 40. Otherwise, power to motor 40 is cut off.

The circuitry shown in FIG. 5 may be powered by AC power supplied atconnector CONN1 ranging from approximately 8 V to approximately 40 V.Diode D1 converts the supplied power from AC to DC (the same powersupply would also function if supplied with DC power). When transistorQ1 is on, capacitor C1 is charged by the power supplied at connectorCONN1 minus the voltage drop across the circuit consisting of diode D1,resistor R1, and transistor Q1. Capacitor C1 will charge when at least2.5V is present at Vcc. Taking into account the voltage drop across D1,R1, and Q1, and the power necessary to run the microprocessor U1 and themotor 40, the circuitry shown in FIG. 5 can operate with a minimum ofapproximately 8V AC. As the supplied voltage is increased, capacitor C1will continue to charge and sufficient power will be supplied to themicroprocessor U1 and to the motor 40.

FIG. 6 is a flow chart of the process followed by the microprocessor U1in controlling the motor 40. When power to the microprocessor U1 isturned on (step 310), state variables and other parameters areinitialized (step 315). Next, the main control loop is entered. The loopbegins by checking the voltage at the microprocessor's Vdd input, anddetermining whether there is sufficient power to power the motor 40(step 320). The output of the optical sensor U2 is then checked todetermine whether the zone valve 10 is passing in front of the opticalsensor (step 325). The microprocessor U1 then obtains the current stateof switch SW1 (step 330), and detects whether an AC signal is present atpin GP5 (step 335). Next, the microprocessor U1 decides whether or notto continue charging capacitor C1 (step 340).

In steps 345-365, the microprocessor U1 decides whether the motor 40should be turned on or off. If the zone valve 10 is normally closed(decision step 345), then the Result register of the microprocessor U1is assigned the value OPTO XOR AC (step 355). If the zone valve 10 isnormally open, (as indicated by switch SW1 being in position 1)(decision step 345), then the OPTO flag is toggled (step 350) beforeassigning to the Result register the value OPTO XOR AC (step 355). AResult register value of TRUE indicates that, if there is sufficientpower, the motor 40 should be turned on. A Result register value ofFALSE indicates that the motor 40 should be turned off.

The process 300 shown in FIG. 6 is now described in more detail.

Referring to FIG. 7, initialization (step 315) proceeds as follows.First, the optical sensor U2 is turned off by de-asserting pin GP0 (step410), in order to conserve power. Next, a flag V_READY, which is used toindicate whether the capacitor C1 has been fully charged, is initializedto FALSE (step 415). A variable AC_PREVIOUS, used by the method of FIG.11 and described in more detail below, is initialized to LO (step 417).Next, the motor 40 is turned off by de-asserting pin GP4 in order toconserve power (step 420). Next, if pin GP5 is HI (decision step 425),indicating the possible presence of an AC signal (or DC signal in theevent that the power supplied to the actuator is DC instead of AC), themicroprocessor U1 delays for one tenth of a second, and then checks pinGP5 again to verify the presence of an AC (or DC) signal (step 440). Ifpin GP5 is not HI during both steps 425 and 440, then the presence of anAC signal has not been verified, and the microprocessor U1 goes intosleep mode (step 430). Once in sleep mode, the microprocessor U1 willwake up again in approximately one second and begin again at step 315.If pin GP5 is HI at steps 425 and 440, then control proceeds to FIG. 9(step 445).

Note that if an AC signal is present and the microprocessor U1 is eitherturned off or in sleep mode, then pin GP2 will act as an open circuit(exhibit high impedance), in which case transistor Q1 will turn on,allowing the AC signal to charge capacitor C1.

Referring to FIG. 8, the microprocessor U1 estimates the voltage at pinVdd by as follows. First, a local variable COUNT is initialized with avalue of 25, and a local variable VCNT is initialized with a value ofzero (step 510). Next, the microprocessor U1 determines whether pin GP1is HI (decision step 515). If GP1 is HI, then VCNT is incremented (step520). This process repeats 25 times (steps 515-530). Whether pin GP1 isHI is an indicator of the voltage at pin Vdd because pins GP1 and Vddare internally connected by a single 25 kΩ resistor (not shown). Themicroprocessor U1 estimates the voltage Vdd as Voltage=2.3+0.1 * VCNT(step 535). If Voltage >2.5 (decision step 540), indicating that thecapacitor C1 has been fully charged, then a flag V_READY is set to TRUE(step 545). Otherwise, the V_READY flag is set to FALSE (step 550).

FIG. 9 shows a method used by the microprocessor U1 to determine whetherthe optical sensor U2 is blocked. The result of the method of FIG. 9 isto set the OPTO flag to TRUE if the optical sensor U2 is not blocked,and to set the OPTO flag to FALSE if the sensor is blocked. First, powerto the optical sensor U2 is turned on by asserting pin GP0 (step 610).Next, an arbitrary 8-bit binary code is transmitted through pin GP0, onebit at a time (step 615). As the microprocessor U1 transmits the code,the microprocessor U1 monitors the input at pin GP1. If the value of thebit received at pin GP1 is the same as the value of the bit transmittedat pin GP0, then the optical sensor is not blocked. If all of the bitsin the transmitted code are correctly received at pin GP1 (decision step620), then the OPTO flag is assigned a value of TRUE (step 630).Otherwise, the OPTO flag is assigned a value of FALSE (Step 625). Ineither case, the power to the optical sensor U2 is then turned off byde-asserting pin GP0 (step 635). Eight bits, rather than a single bit,are transmitted and tested in order to take into account manufacturingimperfections in the zone valve 10 which might cause spurious readingsof the optical sensor when an edge of the drive member 47 is in front ofthe sensor. Requiring that eight consecutive readings of the opticalsensor output all match the expected readings ensures that the zonevalve 10 has completed a state transition.

Referring to FIG. 10, the NORMALLY_OPEN flag, which indicates whetherthe zone valve 10 is normally open or normally closed, is set asfollows. If pin GP3 is HI (decision step 710), then the NORMALLY_OPENflag is assigned a value of TRUE (step 715). Otherwise, theNORMALLY_OPEN flag is assigned a value of FALSE (step 720).

Referring to FIG. 11, a flag AC is assigned a value of TRUE when an ACsignal is detected at pin GP5, and is assigned a value of FALSE when noAC signal is detected for a period of time. In addition, a flagAC_TRANSITION is assigned a value of TRUE when the flag AC changesvalue, and is assigned a value of FALSE otherwise.

More specifically, the values of AC and AC_TRANSITION are assigned asfollows. First, the microprocessor U1 determines whether pin GP5 is HI(decision step 810). If it is not, then the microprocessor U1initializes a variable COUNT to a value of 150 and assigns the valueTRUE to the flag AC (step 815). Then, if AC is not equal to AC_PREVIOUS(decision step 820), then the value of AC_TRANSITION is set to TRUE(step 835). Otherwise, the value of AC_TRANSITION is set to FALSE (step837). The value of AC_PREVIOUS is then assigned the value of AC (step840).

If pin GP5 is HI (decision step 810), then COUNT is decremented (step825). If COUNT=0 (decision step 830), then AC is set to FALSE (step845).

Referring to FIG. 12, the microprocessor U1 decides whether to continuecharging capacitor C1 as follows. If V_READY is FALSE (see FIG. 8)(decision step 910), then capacitor C1 is charged by putting pin GP2into input mode, causing pin GP2 to act like an open circuit (step 915).If V_READY is TRUE (decision step 910), then the microprocessor U1 stopscharging capacitor C1 by putting pin GP2 into output mode and assertingLO, causing pin GP2 to act like a short circuit (step 920). This turnsoff transistor Q1, which prevents capacitor C1 from charging.

After the method of FIG. 12 has completed, the microprocessor decideswhether the motor should be turned on or off. If the switch SW1 is inposition 1, indicating that the zone valve 10 is normally open (decisionstep 345), then the OPTO flag is toggled (step 350). Then, the Resultregister is assigned the value OPTO XOR AC. A Result value of TRUEindicates that the motor 40 should be turned on, if there is sufficientpower. A Result value of FALSE indicates that the motor 40 should beturned off. The expression OPTO XOR AC results in the appropriate valuesfor the Result register as follows.

TABLE 1 Result Result (Normally (Normally SENSOR OPTO AC Open) Closed)BLOCKED FALSE FALSE TRUE FALSE BLOCKED FALSE TRUE FALSE TRUE UNBLOCKEDTRUE FALSE FALSE TRUE UNBLOCKED TRUE TRUE TRUE FALSE

Referring to Table 1, consider, for example, the case in which the zonevalve 10 is normally closed (i.e., switch SW1 is in position 2). In thiscase, if OPTO is FALSE (i.e., the optical sensor is blocked, indicatingthat the zone valve 10 is closed) and AC is FALSE (indicating that thethermostat is not requesting that the zone valve 10 change its state),then the zone valve 10 is in the correct position. Therefore, the valueof Result is FALSE, indicating that the motor should be turned off.Consider next, for example, the case in which the zone valve 10 isnormally open (i.e., switch SW1 is in position 1). In this case, if OPTOis FALSE (i.e., the optical sensor is blocked, indicating that the zonevalve 10 is closed) and AC is FALSE (indicating that the thermostat isnot requesting that the zone valve 10 change its state), then the zonevalve 10 should return to its default position of open. Therefore, thevalue of Result is TRUE, indicating that the motor 40 should be turnedon. The values in the remaining cells in Table 1 can be verifiedsimilarly.

Once the value of Result has been calculated, the microprocessor U1decides whether to actually provide power to the motor 40 as shown inFIG. 13. If V_READY is TRUE, then pin GP4 is asserted, turning the motor40 on (step 1015). If V_READY is FALSE, then the motor 40 is not turnedon. This ensures that the motor 40 is not turned on unless there issufficient power.

Other embodiments of the invention are within the scope of the followingclaims. For example, the invention may be used to provide other types ofvalves, e.g., a mixing valve or a two-way valve.

In the case of a mixing valve, a different ball element, with a centralaperture communicating with port 37 c (FIG. 1) at the base of the valvebody, replaces the ball element shown in FIG. 1. Ports 37 a, 37 b becomeinlets (e.g., hot and cold water) and port 37 c is the outlet. Theleft-to-right aperture in the ball element, which is straight in theembodiment of FIG. 1, becomes curved so that rotation of the ballelement causes a change in the proportions of fluid flowing through thevalve from the two ports. By using a noncircular cross motion for theaperture (e.g., tear drop), a linear relationship can be achievedbetween ball rotation and flow. Projections 72, 74 are also configureddifferently so that the output of the optical sensor changes state afterthe ball element has turned sufficiently to complete close off one ofthe ports. E.g., one of the projections might block the sensor toindicate that port 37 a was shutoff, and the other of the projectionsmight do the same for port 37 b. In operation, movements of the mixingvalve are controlled by activating motor 40 for short durations to makesmall adjustments to the position of the ball element. Polarity of thepower is reversed to change the direction of rotation. During thesemovements the optical sensor does not provide information; it is onlywhen the ball element has reached a point at which one or the other ofthe ports is closed off that the sensor functions. In effect, itreplaces the mechanical stop that would be found in a conventionalmixing valve.

For a two-way valve, the right-to-left aperture in the ball elementextends from the center of the ball in only one direction, so that byrotating the valve 180 degrees, the central port 37 c can be connectedto one or the other of ports 37 a, 37 b. The same configuration ofprojections 72, 74 can be used, or alternatively, a single projectionextending 180 degrees could be substituted.

What is claimed is:
 1. An electrically-operated actuator for actuating avalve in a heating or cooling flow system, the actuator being normallysupplied with electrical power from a main source of electrical power,the valve having a first position in which fluid flow may occur alongone path and a second position in which fluid flow is either blocked ormay occur along a second path, at least one of the positions being afail safe position to which the valve should return in the event of lossof electrical power from the main electrical power source, the actuatorcomprising a motor coupled to the valve, wherein rotation of the motorchanges the position of the valve from one of the first and secondpositions to the other of the positions; a switch controlling thedelivery of electrical power to the motor, the switch having a closedposition in which electrical power is delivered to the motor and an openposition in which power is not delivered; one or more sensors configuredto detect the arrival of the valve at the first and second positions; anelectrical power storage element providing power for driving the motor;and circuitry connected to the one or more sensors and to the switch,the circuitry being configured to respond to the detection by the one ormore sensors of the arrival of the valve at one of the first and secondpositions by opening the switch to stop delivery of power to the motor,and the circuitry being further configured so that in the event of lossof electrical power from the main electrical power source, electricalpower from the electrical power storage element is used to return thevalve to the fail safe position, by powering the motor until the one ormore sensors detects arrival of the valve at the fail safe position, atwhich time the switch is opened to stop delivery of power to the motor,to leave the valve in the fail safe position, and wherein the valve isreturned to the fail safe position and stopped at the fail safe positionwithout use of a mechanical stop.
 2. The actuator of claim 1, whereinthe sensor is configured so that the output of the sensor changes stateupon the arrival of the valve at a desired position.
 3. The actuator ofclaim 2, wherein the sensor has two states, and a change of state in theoutput occurs at approximately the moment when the valve, having begunto move from one of the first and second positions, reaches the other ofthe positions.
 4. The actuator of claim 1, wherein the motor rotates thevalve in a single direction.
 5. The actuator of claim 1, wherein theelectrical power storage element is a capacitor.
 6. The actuator ofclaim 1 wherein the circuitry comprises an integrated circuit chip. 7.The actuator of claim 4, wherein the valve is a ball valve.
 8. Theactuator of claim 1, wherein the sensor is an optical sensor.
 9. Theactuator of claim 8, wherein projections on a member that rotates withrotation of the valve cause the sensor to become blocked and unblocked,and arrival of the valve at a position corresponds to blockage of thesensor by a projection either ceasing or beginning.
 10. The actuator ofclaim 1, further comprising a clutch for manually rotating the valve.11. The actuator of claim 10, wherein a position of an externallyvisible element indicates the angular position of the valve.
 12. Theactuator of claim 1, wherein a spring is not required to return thevalve to a previous state.
 13. The valve of claim 1, wherein the valveis a zone valve for use in a hydronic system, and the valve comprising aball element; a valve casing enclosing a ball element; a valve seat incontact with the ball element and the valve casing, the valve seathaving a notch to receive an O-ring; an O-ring installed in the notch; ametallic, springy washer positioned in a compressed state within thevalve casing in such a configuration as to provide an approximatelyconstant axial force on the valve seat; and wherein the notch is shapedso that the axial force causes the O-ring installed in the notch to becompressed to improve a seal between the valve seat and an internal boreof the valve casing.
 14. The actuator of claim 1, further comprising adefault-position selection switch connected to the circuitry, whereinthe default-position selection switch is movable between a positioncorresponding to the valve being normally open and a positioncorresponding to the valve being normally closed, and wherein thecircuitry is configured to respond to changes in the position of theselection switch to change the default position of the valve.
 15. Theactuator of claim 1, further comprising a worm gear drive for couplingthe motor to the valve.
 16. The valve of claim 1, wherein the circuitryis further configured to operate the actuator as follows: prior toinitiating movement of the valve, determining the charge on a capacitivepower source that forms the electrical power storage element anddetermining the energy required to complete the valve movementprescribed; deciding to initiate movement if the charge on thecapacitive power source is sufficient to provide the energy required tocomplete the movement; and deciding not to initiate movement if thecharge on the capacitive power source is insufficient to provide theenergy required to complete the movement.
 17. The valve of claim 1,further comprising a gear assembly coupling the motor to the valve,wherein the gear assembly includes a worm gear; and a knob shaped to beturned manually either by grasping or by use of a tool; a clutchassembly connecting the knob to the valve stem and to the gear assembly,wherein the clutch assembly can be moved between engaged and disengagedmodes, wherein in the engaged mode the gear assembly and worm gear areengaged with the valve stem so that the motor can turn the valve, and inthe disengaged mode the gear assembly and worm gear are disengaged fromthe valve stem so that the valve can be turned using the knob.
 18. Theactuator of claim 17, wherein the clutch assembly is disengaged bypushing the knob axially.
 19. The actuator of claim 18, wherein theclutch assembly comprises teeth on two rotating members that areseparated by axial motion of the knob to disengage the clutch.
 20. Theactuator of claim 17 wherein the knob has a marking indicating theposition of the valve.
 21. The actuator of claim 4, wherein the valve isa butterfly valve.
 22. The actuator of claim 1, wherein the valve is avalve configured for a hydronic heating or cooling system.
 23. Theactuator of claim 1, wherein there is a single sensor that detectsarrival of the valve at both the first and second positions.
 24. Theactuator of claim 1, wherein the electrical power storage element is acapacitive storage device.
 25. The actuator of claim 24, wherein thecapacitive storage device is a capacitor.